Most people limit their home stereo setup to a receiver and speakers, but if you're doing this, you're not getting the most out of your sound. Amplifiers and equalizers allow you to control and shape audio playback, giving you precise control over sound, whether you're shaking your windows with home theater or coaxing the nuances out of classical performances. As you tune up your stereo system, you'll need to be careful to keep everything in balance.
Impedance and Maximum Power
Most receivers have a built-in amplifier that will produce enough decibels to annoy your neighbors. Shopping for raw power is one way to go, but if you have speakers, you need to be certain your new amplifier is compatible with them.
Two important factors when matching an amplifier to speakers are impedance and power requirements. If you buy an amplifier that is too powerful for your speakers, your speakers may become damaged or destroyed and your home stereo system is ruined. Speakers all have a range of acceptable power inputs, and you should shop for an amplifier with power output that fits within the acceptable range for speakers. Some home audio amplifiers produce more than 100 watts per channel. If you match that amplifier with speakers rated for 75 watts per channel, you risk tearing the speaker membranes or frying the electronics in the speakers. Inversely, choosing an amplifier that provides only 50 watts per channel means that your speakers will be underpowered, and you'll have to crank your amplifier inordinately high just to be able to hear things.
Impedance measures the amount of resistance that circuits provide to the flow of signals. Home audio amplifiers are generally rated at 4, 8 or 16 ohms. This does not mean that the home audio amplifier generates 4 ohms of impedance, but that it wants to work with a 4-ohm speaker. Low impedance means less resistance to the flow of electrical current. Using a 4-ohm amplifier with 16-ohm speakers can destroy the electronics in the speakers. It's best to match impedances, although low-impedance speakers will work with higher-impedance amplifiers.
Choosing an Amplifier
The first and biggest quality indicator for an amplifier is the Total Harmonic Distortion, or THD. Amplifying an audio signal results in distortion, and THD measures how much distortion you can expect. Most THD ratings are below 1%, but for maximum quality, look for a THD that is near or below 0.1%.
The next thing to consider is frequency response, or the range of sounds the amplifier can produce. The best home stereo systems reproduce sounds from 20Hz at the low end to 20,000Hz at the high end. While this gives you the full range of reproducible sound, most adults lose the ability hear frequencies above 15,000Hz, so you might not need the full range. In general, rock enthusiasts and movie lovers should look for good bass response (below 200Hz), while jazz and classical fans should choose high-frequency response over bass.
You'll also want to pay attention to the connections an amplifier offers. How many devices will you need to connect? If you've got a turntable, you'll need to find a home stereo that offers a built-in preamp, which is missing on most systems. RCA cable connections are still common, but it's worth looking for higher-quality digital connections as well as USB and TOSLINK ports for computers and MP3 players.
Adding a Graphic Equalizer
A graphic equalizer boosts or reduces audio signals at specific frequencies. The best graphic equalizers are stand-alone models that allow you to individually adjust audio signals. There are programmable equalizers available as well, but most consumers prefer a graphic equalizer, which uses a series of sliders to provide a visual representation of how the sound is shaped.
Equalizers operate on a series of bands, and each band represents a specific frequency or frequency range. The more bands your equalizer has, the more control you have over the sound of your home audio setup. A 30-band home audio equalizer gives you an opportunity to adjust up to 30 different frequencies, while a 10-band equalizer gives you much more rudimentary control over just 10 different frequencies.
With graphic equalizers, setting the sliders in the center of the available range, usually indicated by a dark line, produces no effect and allows the frequency to pass through untouched. Pushing the sliders up increases the amount of signal for that frequency, while pushing them below the line reduces the signal. With practice, you can use a graphic equalizer to emphasize the parts of a recording that you most want to hear. A common use is to enhance the vocals in rock and pop music, which typically live in a range from 300 to 3,000 Hz.
A good equalizer can minimize problems caused by an amplifier, but it can't do away with them entirely or add signal that isn't there. If you're thinking about adding an equalizer to your current system, match the equalizer's bands as closely as possible to the frequency range of your amplifier. You should also make sure your amplifier has a plain stereo or "plate" setting, since equalizers work best with unfiltered signals.
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